When using a pulsed laser for patterned material deposition, methods fall into two general categories: laser-induced forward transfer (LIFT) and laser-induced backward transfer (LIBT). The ablated material is transferred to the receiving substrate in the same direction with LIFT, or in a reverse direction relative to the incident laser with LIBT. In LIFT, a target film needs to be deposited on a laser-transparent supporting substrate. The receiving substrate is placed facing the target film. The laser beam, incident from the uncoated side of the target supporting substrate, causes ablation in the target film. The ablated material is transferred forwardly in the same direction as the laser, and to the receiving substrate. In a LIBT setup, the geometry is reversed. The laser is guided through the laser-transparent receiving substrate first and focused on the target. The target can be a plate made of the desired target material. Upon ablation, the ablated material is transferred backwardly, in a reverse direction to the incident laser beam, and deposited on the receiving substrate.
Several LIFT methods are disclosed in, for example, U.S. Pat. Nos. 4,752,455 and 6,159,832 issued to Mayer, U.S. Pat. No. 4,987,006 issued to Williams et al., U.S. Pat. Nos. 6,177,151 and 6,766,764 issued to Chrisey et al. A few LIBT methods are described in U.S. Pat. No. 5,173,441 issued to Yu et al, Japan patent 2005-79245 issued to Hanada et al., and US patent application 2007/0243328 to Liu et al.
Laser-induced-plasma assisted ablation has been used for color marking of metal targets, as disclosed by Hanata et al, “Colour marking of transparent materials by laser-induced-plasma-assisted ablation (LIPAA)”, Journal of Physics: Conference Series 59 (2007), 687-690. Various lasers were tested, and produced various picosecond, nanosecond, and femtosecond outputs, with a maximum repetition rate of 10 KHz. For this RGB process it was concluded that a conventional nanosecond pulse width has great potential for high-quality and cost effective marking in the laser-marking industry.
An object of the above methods is precise and patterned deposition of materials. If applied to printing, these methods are binary and would provide an on/off effect or a visually black/white effect. In order to print a bitmap image over a large gray scale range, two requirements need to be satisfied: (i) sufficient number of gray scale levels and (ii) a practically acceptable speed of printing.
A recent international patent application, WO 2008/091898 by Shah et al., assigned to the assignee of the present application, discloses a method of ultrashort pulsed laser printing of images on solid surfaces. This method is based on surface texturing induced by ultrashort pulsed laser interaction with solid surfaces. In a range of laser fluence and exposure time (average power per unit area), several types of surface textures can be produced after laser irradiation, including ripples, pillars, pores and many types of random micro-protrusions. A controlled arrangement of these textures produces a visual effect of gray scale by scattering, trapping, and absorbing light. This method does not involve material transfer from a target to a substrate.
LIFT, LIBT, and LIPAA systems have utilized Nd:YAG, Ti:Sapphire at a 1 kHz repetition rate, and up to about 10 KHz with NdYVO4 based systems. Forming patterns or images at high resolution on a macroscopic scale could take up to a thousand minutes as a result of the low repetition rates, limiting the application of these methods. Moreover, as set forth above, many systems are limited to production of binary patterns.